diff --git a/doc/03-cli.md b/doc/03-cli.md
index 37325f2a6..7334c0516 100644
--- a/doc/03-cli.md
+++ b/doc/03-cli.md
@@ -607,6 +607,9 @@ you may have to run the command with `root` privileges
 sudo -H composer self-update
 ```
 
+If Composer was not installed as a PHAR, this command is not available.
+(This is sometimes the case when Composer was installed by an operating system package manager.)
+
 ### Options
 
 * **--rollback (-r):** Rollback to the last version you had installed.